In fabricating semiconductor devices, desired patterns formed on a photo mask (reticle), with the photolithography, are transferred through a reducing optical system to a substrate including a photosensitive resist formed thereof. Then, the latent images of the transferred patterns are patterned utilizing the difference in the rate of solution by developing liquid between the exposed portion and the non-exposed portion and etching is applied to the transferred patterns to process desired wiring layers.
In order to transfer fine patterns with high accuracy with an exposing technique, the exposure light wavelength and the reticle construction are optimized and also the influences of adjacent patterns are calculated and corrected. Such corrections are referred to as optical proximity effect corrections (OPC), wherein the amount of correction is calculated by determining, from calculations or experiments, the influences of optical proximity effects (OPE), in consideration of illumination conditions (NA, Sigma) and exposure conditions (the resist material and the exposure light wavelength, etc.) of the exposing apparatus, and thus reticle dimensions are corrected to correct the transferred pattern images.
As a method for correcting mask-pattern utilizing such OPCs, for example, there is a method disclosed in Patent Document 1 which will be listed later. The method disclosed in Patent Document 1 creates OPC tables for respective pattern densities, calculates the pattern densities of subregions, the sub regions being created by dividing the exposure shot region into regions of a dimension of about a few hundred micrometers, and performs corrections utilizing different OPC tables for respective pattern density values.
However, there are flares in exposing apparatuses, which are components which can not be corrected by OPCs. Such flares in exposing apparatuses are caused by fine concavities and convexities on lenses, fluctuations in the refractive index of lenses and light reflected and scattered by the wafer surface. Such flares cause an amount of offset exposure corresponding to the opening ratio around the mask patterns, resulting in fluctuations in the transferred-pattern dimensions or reduction of the exposure margin.
More recently, occurrences of local flares depending on the conditions around respective patterns have been acknowledged as a problem. Such flares are referred to as so-called local flares and have been main cause of occurrences of unexpected fluctuations in the shapes and the line widths of transferred patterns since the distinctiveness of the lens material depending on the wavelength of used exposure light (short wavelengths represented as 193 nm) causes differences in the condition of light applied to patterns corresponding to the opening ratio around the patterns. Local flares caused by a pattern in a mask have influences within an area around the pattern with a dimension of about 50 micrometers. However, the area within which local flares have influences may vary in the future depending on the generation of exposing apparatuses and the exposure light wavelength. In addition, the influences of local flares vary depending on the portion on a photo mask since the influences of local flares vary corresponding to the opening ratio around the pattern. Therefore, the amount of fluctuations in the line width of a resist pattern varies depending on the position. Therefore, it is extremely difficult to correct the patterns of a photo mask taking account of the influences of local flares.
Further, the method of Patent Document 1 assumes globally occurring dimension fluctuations and therefore provides equal correction values for patterns with the same distance to adjacent patterns within sub regions of a dimension of about a few hundred micrometers, which may induce correction errors. For example, the sub regions 201 partitioned by solid lines in FIG. 11A and the sub regions 201 partitioned by solid lines in FIG. 11B have the same pattern density, although they have different placements of patterns 202 within the respective sub regions 201. Thus, the correction values for line patterns 203 placed at the center in FIG. 11A and the line patterns 203 placed at the center in FIG. 11B will be equal. This may cause correction errors in some cases and may also cause larger correction errors near the boundaries of the sub regions 201.
[Patent Document 1] Japanese Patent Application Laid-open No. 2002-148779
[Patent Document 2] Japanese Patent Application Laid-open No. 2000-235248
[Patent Document 3] Japanese Patent Application Laid-open No. Hei 09-319067
[Patent Document 4] Japanese Patent Application Laid-open No. 2002-311563